Todd Gurley was the key to the Los Angeles Rams’ offensive transformation last season, and the Rams have rewarded their star running back with a game-changing contract.

The NFL’s offensive player of the year agreed to a four-year, $60 million contract extension through 2023 with the Rams on Tuesday.

A person with knowledge of the deal, speaking on condition of anonymity because the terms weren’t publicly announced, confirmed to The Associated Press that Gurley’s contract extension contains $45 million in guaranteed money, a $20 million signing bonus and the NFL’s largest average annual value for a running back contract. ESPN first reported the terms.

General manager Les Snead said the Rams wanted “to get ahead of the curve” by signing Gurley two years before his rookie contract expires. They’ve also set a new benchmark for running back salaries to secure a cornerstone of a team with Super Bowl aspirations.

“He’s a big part of who we are and where we’re going,” Snead said. “It’s not only Todd, but a lot of guys we want to make Rams for a long time and be part of our core.”

Gurley isn’t due to report to training camp at UC Irvine until Wednesday. His first public reaction was to post a black-and-white Instagram photo of himself with a broad smile and the caption: “Amazing...”

Gurley was a league standout in his third NFL season while playing in first-year coach Sean McVay’s explosive offense. He finished second in the NFL with 1,305 yards rushing and 13 touchdowns while catching 64 passes for 788 yards and six more TDs.

“What a special player he is,” McVay said. “I think last year’s production isn’t really a (complete) reflection of the value he provides, because he did such a great job, but he’s so much more than that to our team — the way that he competes in protection, the way that he works, and the way that rubs off on his teammates.”

Along with being a handsome reward for a burgeoning NFL star, Gurley’s deal sets a new standard in the market for ball-carriers such as Dallas’ Ezekiel Elliott and Arizona’s David Johnson — and for Pittsburgh’s Le’Veon Bell after he plays out this season on the franchise tag.

Bell, who received public support from Gurley during his contentious recent negotiations with the Steelers, returned the love on Twitter, along with an additional comment about his own failure to get a big contract in Pittsburgh: “lol and ppl thought I was trippin?”

Gurley was the offensive rookie of the year in 2015 for the Rams, rewarding their gamble on him with the 10th overall pick. He overcame a torn knee ligament in his final season with the Georgia Bulldogs to rush for 1,106 yards with St. Louis.

Gurley struggled as part of the NFL’s worst offense during the Rams’ relocation season in 2016, with his yards-per-carry average dropping from 4.8 to 3.2.

That average shot right back up to 4.7 last season while he starred for the NFC West champions behind a stout offensive line that had the same starters for 15 consecutive weeks. Gurley likely would have won the NFL rushing title if McVay hadn’t rested him for the Rams’ regular-season finale ahead of their playoff loss to Atlanta.

Gurley has also grown swiftly as a receiver in his three seasons, increasing his catches from 21 as a rookie to 43 and then 64 last season.

Gurley’s contributions to the Rams last season drew praise from Eric Dickerson, the most popular player in Los Angeles Rams history for his 1980s exploits as a record-setting running back. Steven Jackson, the Rams’ franchise rushing leader, also hailed Gurley’s contract Tuesday on Twitter.

“Great to see Les Snead and the @RamsNFL front office prioritize the running game!” Jackson tweeted. “To not only draft (Gurley) early, but now lock him into a long-term deal to ensure he continues to thrive as a Ram is huge!”

The Rams haven’t been shy about securing several key pieces of their talented roster during this offseason, which began with the high-profile additions of Ndamukong Suh and cornerbacks Marcus Peters and Aqib Talib. Last week, Los Angeles signed receiver Brandin Cooks to a five-year, $80 million extension before he catches his first pass with the Rams.

But an even bigger issue still looms for Los Angeles: defensive tackle Aaron Donald still doesn’t have a new contract two days before the first practice of training camp.

Donald, the NFL’s defensive player of the year, and the Rams have been working on a long-term extension since early last year. The powerhouse lineman is seeking a game-changing contract that would make him one of the NFL’s highest-paid players, but hasn’t yet been successful.

Donald skipped all of training camp last year in a holdout, and he missed all of the Rams’ offseason activities this spring.

Snead and McVay acknowledged Donald might not report to training camp Wednesday, but they weren’t sure about his plans. Snead is still in active negotiations with Donald’s representatives at CAA Sports.

“I do know we’ve still got time to get something done,” Snead said.

Donald is under contract for this season for nearly $6.9 million in the fifth year of his rookie contract.

“We’re simultaneously working to make Aaron a Ram a long time,” Snead said. “That’s the goal. Aaron is a big part of who we are, where we want to go, but the details and all that, we’re going to continue the course of keeping them in-house.”